Build.scala

import sbt._
import Keys._
import play.Project._

object ApplicationBuild extends Build {

  val appName         = "javatest"
  val appVersion      = "1.0-SNAPSHOT"

  val appDependencies = Seq(
    // Add your project dependencies here,
    javaCore,
    javaJdbc,
    javaEbean
  )

  import VersionInfoPlugin._ 
  //add this: ^ import the plugin
  val main = play.Project(appName, appVersion, appDependencies).settings(
    // Add your own project settings here      
  ).settings(versionInfoSettings: _*)
  //add this:  ^ enable the plugin
  .settings(
    versionInfoPackage := "com.mycompany.utils"
   //add this:             ^ the package for the generated class
  )

}

VersionInfo.scala

import sbt._
import Keys._

object VersionInfoPlugin extends Plugin {
  val versionInfoPackage = SettingKey[String]("version-info-package")
  val versionInfoClassTask = TaskKey[Seq[java.io.File]]("version-info-class", "writes a java class VersionInfo with information about the versionInfo to sourceManaged")
  val versionInfo = TaskKey[String]("version-info", "the current versionInfo")

  val versionInfoSettings = Seq(
    versionInfo <<= version map { version =>
      Option(System.getProperty("version")).getOrElse{ //use property version if found
        version
      }
    },
    versionInfoClassTask <<= (sourceManaged in Compile, versionInfoPackage, versionInfo) map { (srcDir, versionInfoPackage, versionInfo) =>
    // depends on:            ^ source directory,       ^ the package       ^ the version 
      val classString = """
      |package %s;
      |
      |public class VersionInfo {
      |    public static String CURRENT_VERSION = "%s";
      |}""" format (versionInfoPackage, versionInfo) stripMargin

      val path = srcDir.getAbsolutePath + versionInfoPackage.replace(".", java.io.File.separator) + java.io.File.separator + "VersionInfo.java"
      IO.write(file(path), classString)
      Seq(file(path))
    },
    sourceGenerators in Compile <+= versionInfoClassTask
    //add our versionInfoClass to generators so it is picked up by sbt
  )
}